WO2003106724A1

WO2003106724A1 - Steel excellent in machinability

Info

Publication number: WO2003106724A1
Application number: PCT/JP2003/007502
Authority: WO
Inventors: 橋村　雅之; 水野　淳; 平田　浩; 内藤　賢一郎; 萩原　博
Original assignee: 新日本製鐵株式会社
Priority date: 2002-06-14
Filing date: 2003-06-12
Publication date: 2003-12-24
Also published as: JP2004018925A; TW200401041A; CN1659297A; TWI306476B; CN100355927C; KR100683923B1; JP4267260B2; KR20050008823A

Abstract

A steel excellent in machinability, characterized in that it comprises, in mass %, 0.001 to 1.5 % of C, 3 % or less of Si, 0.01 to 3 % of Mn:, 0.001 to 0.2 % of P, 0.0001 to 1.2 % of S, 0.001 to 0.5 % of Zn, 0.0001 to 0.02 % of N, and 0.0005 to 0.05 % of O. Optionally, the steel may further comprise 0.002 to 0.5 % of Sn and/or 0.0005 to 0.05 % of B, which elements are both a machinability imparting element.

Description

Description Steel with excellent machinability Technical field

The present invention relates to steel used for parts such as automobiles and general machines, and more particularly to steel excellent in machinability such as tool life during cutting, cutting surface roughness and chip handling. Background art

General machines and automobiles are manufactured by combining various types of parts, but the parts are often manufactured through a cutting process from the viewpoint of required accuracy and manufacturing efficiency. At that time, cost reduction and improvement in production efficiency are required, and steel is also required to have improved machinability.

SUM23 and SUM24L, which are called low-carbon free-cutting steels with less than 0.2% C, have been developed with emphasis on machinability. It has been known that it is effective to add machinability improving elements such as S and Pb to improve machinability. However, in recent years, Pb has tended to avoid its use as an environmental burden, and its use has been reduced.

Until now, when Pb is not added, a method has been used to improve the machinability by forming soft inclusions in a cutting environment like MnS like S. However, the so-called low-carbon lead free-cutting steel SUM24L contains the same amount of S as the low-carbon sulfur free-cutting steel SUM23. Therefore, it is necessary to add more S than before to improve machinability. However, the addition of large amounts of S does not only result in MnS distribution that is effective for improving machinability simply by making MnS coarse, but also causes rolling problems such as rolling flaws in rolling and forging, etc. Cause a lot. In addition, SUM23 Sulfur free-cutting steel, which is used as a base, easily adheres to the cutting edge, causing irregularities on the cutting surface due to the falling-off of the cutting edge and the chip separation phenomenon, deteriorating the surface roughness. Therefore, from the viewpoint of machinability, there is a problem that accuracy is reduced due to deterioration of surface roughness. In terms of chip disposability, it is considered better if chips are short and easy to separate, but simple addition of S has a large ductility of the matrix, so it was not sufficiently divided and could not be improved significantly.

Elements other than S, such as Te, Bi, and P, are also known as machinability improving elements.However, even if machinability can be improved to some extent, cracks are likely to occur during rolling and hot forging. It is said that it is desirable to have as little as possible.

Also, steel containing 0.2% or more of C has a relatively high strength because it contains many alloying elements such as C, Cr, and Mo. In the case of such structural steel, the problem of the formation of the cutting edge and the resulting unevenness (roughness) of the cutting surface is small, and the surface roughness is relatively good because it is originally a hard material. However, if a large amount of S, which is a machinability improving element, is added due to its high basic strength, the resulting MnS will be elongated by rolling or forging, resulting in anisotropy in mechanical properties. Application to parts is greatly restricted. In addition, S is not added to high-strength steel to improve machinability, and in most cases, machinability is sacrificed. Disclosure of the invention

Under the circumstances described above, the present invention reduces both the tool life and surface roughness of so-called low carbon steels with a C content of less than 0.15% while avoiding defects in rolling, forging, and product performance. It is an object of the present invention to provide a steel having improved and excellent machinability. In the case of a structural steel containing 0.15% or more of C and a high-strength steel, the mechanical properties ( Anisotropic And steel with excellent machinability. Cutting is a breaking phenomenon that separates chips, and promoting it is one of the key points. However, as mentioned above, there is a limit to simply increasing S.

Therefore, the present inventors have conducted extensive studies and conducted extensive studies. As a result, not only increasing the amount of S but also including Zn as a basic component embrittles the matrix and facilitates blasting. It has been found that the tool life can be extended and the unevenness of the cutting surface can be suppressed.

The present invention has been made based on the above findings, and the gist is as follows.

(1) In mass%,

C: 0.001-1.5%,

Si: 3% or less,

Mn: 0.01-3%,

P: 0.001 to 0.2%,

S: 0.0001-1.2%,

Zn: 0.001—0.5%,

N: 0.0001-0, 02%,

O: 0.0005-0.05%

A steel excellent in machinability characterized by containing.

(2) The steel excellent in machinability according to the above (1), further comprising Sn: 0.002 to 0.5% by mass%.

(3) The steel excellent in machinability according to the above (1) or (2), further containing B: 0.0005 to 0.05% by mass%.

(4) In addition, the mass ^{_{0/0, Cr: 0.01~ 7}} %, Mo: 0.01~ 3%, V: 0.01~3.0%, Nb: 0.001~0.2%, Ti: 0 · 001~0 · 5%, W:

It is characterized by containing one or more of 0.01 to 3% The steel excellent in machinability according to any one of the above (1) to (3).

(5) Furthermore, mass ⁰ /. Wherein Ni: 0.05 to 7%, Cu: 0.02 to 3% and one or two of them are contained, and when 0.3% or more is contained, Ni% ≥ Cu% is satisfied. A steel excellent in machinability according to any one of (1) to (4).

(6) Furthermore, mass ⁰ /. A1: 0.001 to 2%, Ca: 0002 to 0.01%, Zr: 0.0003 to 0.5%, Mg: 0.0002 to 0.02%, characterized by containing one or more of the following: The steel excellent in machinability according to any one of the above (1) to (5).

(7) In addition, the mass ^{_{0/0, Te: 0.001~0.5%}} , Pb: 0.01~0.7%, Bi: above, characterized in that it contains one or more of from 0.01 to 7% ( 1) A steel excellent in machinability according to any one of the above 6) to 6). BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing an outline of a plunge cutting test, in which (a) shows a plunge cutting test method, and (b) shows a tool movement.

FIG. 2 is a view showing an Ono-type rotary bending test piece with a notch. Fig. 3 is a schematic diagram showing carburizing conditions, (a) is a schematic diagram showing carburizing and quenching, and (b) is a schematic diagram showing normalizing conditions.

BEST MODE FOR CARRYING OUT THE INVENTION

The basic idea of the present invention is to improve machinability without impairing mechanical properties by including Zn as an essential component of steel in addition to S.

That is, Zn is a particularly important element in the present invention. Zn has the effect of embrittlement of steel, has the effect of improving machinability, Has the effect of improving In addition, since it does not take the form of coarse inclusions such as MnS, which is conventionally known, and exists in the matrix, deterioration of mechanical properties can be suppressed to a minimum. This effect is particularly noticeable as anisotropy. Conversely, even if they have similar mechanical properties, good machinability can be obtained when Zn is added. This is thought to be because the embrittlement effect of Zn becomes significant when the temperature rises due to the cutting heat. In addition, it is believed that during cutting, a lubrication effect is created at the tool / workpiece interface. Zn: If less than 0.001%, the effect is small. On the other hand, since Zn is very easy to evaporate during smelting, it is necessary to add a large amount of Zn in order to keep Zn in molten steel and maintain Zn content exceeding 0.5% after solidification. Since it is not industrially feasible in terms of cost, the upper limit was set at 0.5%. Therefore, the range of Zn content in the steel of the present invention is limited to 0.001 to 0.5%.

In addition to Zn, machinability-improving elements such as Sn, B, and Te can be contained, but Sn alone does not improve machinability, and machinability is enhanced by interaction with Zn. Is improved.

The reason for limiting the steel components other than Zn will be described below.

C: 0.001 to 1.5%

C has a significant effect on machinability because it relates to the basic strength of steel and the amount of oxygen in the steel. If the strength is increased by adding a large amount of C, the machinability decreases, so the upper limit was set to 1.5%. On the other hand, it is necessary to control the amount of oxygen appropriately to prevent the formation of hard oxides that reduce machinability and to suppress the adverse effects of solid solution oxygen at high temperatures such as pinholes during the solidification process. . If the C content is simply reduced too much simply by blowing, not only does the cost increase, but also a large amount of oxygen in the steel remains, causing problems such as pinholes. Therefore, the lower limit of 0.001% of C, which can easily prevent problems such as pinholes, was set as the lower limit. Si: 3% or less

Excessive addition of Si lowers the hot ductility and makes rolling and the like difficult, but proper addition imparts mechanical properties and softens oxides to improve machinability. The upper limit is 3%, and if it is more than this, the hot ductility is lowered and rolling becomes difficult, and industrial production becomes difficult. Further, adverse effects such as reduction of machinability due to generation of hard oxides also occur.

Mn: 0.01 to 3.0%

Mn is necessary as a deoxidizing element and to fix and disperse sulfur in steel as MnS. It is also necessary to soften the oxides in steel and make the oxides harmless. The effect depends on the amount of S added, but if it is less than 0.01%, the added S cannot be sufficiently fixed as MnS, and S becomes FeS and becomes brittle. When the amount of Mn increases, the hardness of the substrate increases, and machinability and cold workability decrease. Therefore, the upper limit was set to 3.0%.

P: 0.001 to 0.2%

The upper limit of P must be set to 0.2% because the hardness of the base material increases in steel, which deteriorates not only cold workability but also hot workability and forming properties. On the other hand, the lower limit is set to 0.001%, which is an element that facilitates cutting by embrittlement and is effective in improving machinability.

S: 0.0001 to 1.2%

S binds to Mn and exists as an MnS inclusion. MnS improves machinability, but elongated MnS is one of the causes of anisotropy during forging. Large MnS should be avoided, but a large amount is preferable from the viewpoint of improving machinability. Therefore, it is preferable to finely disperse MnS. To improve machinability, 0.0001% or more is required, and 0.001% or more is preferable. On the other hand, if the content exceeds 1.2%, coarse MnS is inevitably generated, and cracks occur during production due to deterioration of the structural characteristics and hot deformation characteristics due to FeS and the like. N: 0.0001-0.02%

N hardens steel if it is solid solution N. In particular, in cutting, it hardens near the cutting edge due to dynamic strain aging and shortens the tool life, but also has the effect of improving the cutting surface roughness. In combination with B, BN is generated to improve machinability. If the N content is less than 0.0001%, the effect of improving the surface roughness by the dissolved nitrogen and the effect of improving the machinability by BN are not recognized, so the lower limit was set. On the other hand, if the N content exceeds 0.02%, a large amount of solid solution nitrogen is present, and the tool life is rather shortened. In addition, bubbles are generated during the production, causing flaws and the like. Therefore, in the present invention, the upper limit is set to 0.02% at which such adverse effects become remarkable.

O: 0.0005-0.05%

If O is free, it becomes bubbles during cooling and causes pinholes. Control is also required to soften the oxides and suppress hard oxides that are harmful to machinability. In addition, oxides are used as precipitation nuclei when MnS is finely dispersed. If the O content is less than 0.0005%, MnS cannot be sufficiently finely dispersed, and coarse MnS is generated, which adversely affects mechanical properties. Therefore, the lower limit was 0.0005%. Further, if the O content exceeds 0.05%, bubbles are generated during the production and pinholes are formed.

Sn: 0.002 to 0.5%

Sn is a soft metal, and is distributed at grain boundaries and the like in steel and embrittles the steel. This improves machinability. If the content is less than 0.002%, the effect is not recognized. If the content exceeds 0.5%, the steel is embrittled to make mirror making and rolling difficult. Therefore, the range was set to 0.002 to 0.5%.

B: 0.0005-0.05%

B is effective in improving machinability. This effect is not remarkable at less than 0.0005%, and the effect is saturated even if added over 0.05%, Therefore, if too much BN is precipitated, cracking will occur during manufacturing due to deterioration of the mirror-forming properties and hot deformation properties. Therefore, the range was 0.0005 to 0.05%.

Cr: 0.01 to 7%

Cr is an element that imparts hardenability and temper softening resistance. Corrosion resistance can be obtained by adding a large amount. Therefore, it is added to steels that require high strength. In that case, it is necessary to add 0.01% or more. However, if added in large amounts, Cr carbides are formed and become brittle, so the upper limit was set at 7%.

Mo: 0.01-1%

Mo is an element that imparts temper softening resistance and improves hardenability. The effect is not recognized at less than 0.01%, and the effect is saturated even if added over 3%, so the addition range was 0.01% to 3%.

V: 0.01 to 3.0%

V forms carbonitrides and can strengthen the steel by secondary precipitation hardening. If it is less than 0.01%, there is no effect on increasing the strength, and if it exceeds 3%, a large amount of carbonitride precipitates and the mechanical properties are rather impaired, so the upper limit was set.

Nb: 0.001 to 0.2%

Nb also forms carbonitrides and can strengthen the steel by secondary precipitation hardening. If the content is less than 0.001%, there is no effect on increasing the strength. If the content exceeds 0.2%, a large amount of carbonitride precipitates and the mechanical properties are rather impaired.

Ti: 0.001 to 0.5%

Ti also forms carbonitrides and strengthens the steel. It is also a deoxidizing element, and it is possible to improve machinability by forming a soft oxide. You. If less than 0.001%, the effect is not recognized, and even if added over 0.5%, the effect is saturated. Also, Ti becomes a nitride even at high temperatures and suppresses growth of austenite grains. Therefore, the upper limit was set to 0.5%.

W: 0.01-1%

W forms carbonitrides and can strengthen the steel by secondary precipitation hardening. If it is less than 0.01%, there is no effect on increasing the strength, and if it exceeds 3%, coarse carbonitrides are precipitated and the mechanical properties are rather impaired. Therefore, the upper limit was set.

Ni: 0.05 to 7%

Ni is effective in strengthening the fly, improving ductility and improving hardenability and corrosion resistance. If the content is less than 0.05%, the effect is not recognized. Even if the content exceeds 7%, the effect is saturated in terms of mechanical properties, so the upper limit is set.

Cu: 0.02-3%

Cu is effective in strengthening ferrite, improving ductility, improving hardenability, and improving corrosion resistance. If the content is less than 0.02%, the effect is not recognized. Even if added over 3%, the effect is saturated in terms of mechanical properties, so the upper limit is set. In addition, when Cu is added alone, the hot ductility is extremely lowered, which causes troubles such as cracking and rolling problems. When the addition amount exceeds 0.3%, it is preferable to add Ni so that Ni% ≥ Cu% in order to avoid manufacturing trouble.

A1: 0.001 to 2%

A1, the steel in our deoxidizing element forming the A1 ₂ 0 ₃ or A1N. This is effective for preventing the austenite grain size from becoming coarse during quenching and for improving toughness. However, if the content is less than 0.001%, the effect is not recognized.If the content is more than 2%, coarse inclusions are generated, and the mechanical properties are rather deteriorated. You. Furthermore A1 ₂ 0 ₃ will cause the tool damage during cutting so hard, may promote wear. Therefore austenite coarsening effect of such grains is saturated, and the upper limit of 2% of adverse effects A1 ₂ 0 ₃ becomes remarkable. Particularly preferred to Rukoto to 0.015% or less that does not produce a large amount of A1 ₂ 0 ₃ in the case of priority the machinability is preferably 0.005% or less in the case of further prioritize softening oxide .

Ca: 0.0002-0.01%

Ca is a deoxidizing element that generates soft oxides and not only improves machinability, but also dissolves in MnS to reduce its deformability, and MnS shape even when rolled or hot forged Has the function of suppressing distraction. Therefore, it is an effective element for reducing anisotropy. If the content is less than 0.0002%, the effect is not remarkable. Even if the content exceeds 0.01%, not only the yield will be extremely deteriorated, but also a large amount of hard Ca0, CaS, etc. will be generated and the coating will be damaged. Decreases machinability. Therefore, the component range was defined as 0.0002 to 0.01%.

Zr: 0.0003-0.5%

Zr is a deoxidizing element and produces an oxide. The oxides serve as precipitation nuclei for MnS and are effective in fine and uniform dispersion of MnS. In addition, it has the function of dissolving in MnS to reduce its deformability, and suppressing the elongation of the MnS shape even in rolling or hot forging. Therefore, it is an element effective for reducing anisotropy. 0. The effect is less than 0,003% is not significant, not only the yield be added exceeds 5% 0.5 becomes extremely poor to generate such a large amount Zr0 ₂ and ZrS hard, cutting rather be Reduce the nature. Therefore, the range of components was specified to be 0.0003 to 0.5%.

Mg: 0.0002-0.02%

Mg is a deoxidizing element and produces oxides. The oxides serve as precipitation nuclei for MnS and are effective in fine and uniform dispersion of MnS. Therefore, it is an effective element for reducing anisotropy. Below 0.00002%, the effect is not noticeable However, even if added in excess of 0.02%, the yield will be extremely poor and the effect will be saturated. Therefore, the component range was defined as 0.0002 to 0.02%.

Te: 0.001 to 0.5%

Te is a machinability improving element. In addition, the formation of MnTe and the coexistence with MnS have the effect of reducing the deformability of MnS and suppressing the elongation of the MnS shape. Therefore, it is an element effective for reducing anisotropy. This effect is not observed at less than 0.001%, and saturates at more than 0.5%.

Pb, Bi: 0.01 to 0.7%

Pb and Bi are elements that are effective in improving machinability. The effect is not recognized at less than 0.01%, and when added over 0.7%, not only does the machinability improvement effect saturate, but also the hot forging properties deteriorate and cause flaws. Cheap. Therefore, the respective contents were set to 0.01 to 0.7%. Example

The effects of the present invention will be described with reference to examples. Some of the test materials having the chemical components shown in Table 1 were melted in a 270 t converter, then disassembled and rolled into billets, and further rolled into φ50 mm steel bars. The others were melted and rolled in a 2 t vacuum melting furnace. For the evaluation of the machinability of the materials shown in Examples 1 to 40 in Table 2, the cutting conditions are shown in Table 3 in the drilling test. The machinability was evaluated at the highest cutting speed (so-called VL1000) that can cut to the accumulated hole depth lOOmni.

Furthermore, the surface roughness was evaluated by so-called plunge cutting, in which the tool shape was transferred by a parting-off tool. Figure 1 shows the outline of the experimental method. That is, as shown in Fig. 1 (a), the test material 2 rotating in the cutting direction 1 is cut by the tool 3, and as shown in Fig. 1 (b), the tool 3 is moved to To form Table 4 shows the cutting conditions. In the experiment, the surface roughness (10-point surface roughness Rz wm) when machining 200 grooves was measured. Specified. Regarding the chip disposability shown in Table 2, the chip has a curl shape, but if the curl is less than 5 turns and the chip breaks and short chips are generated, “〇” indicates that The case where a long chip that does not break even when exceeding this is generated is denoted as “X”.

table 1

Example Chemical component (mas _S %)

No. Category C Si Mn P S Zn Sn B Te Pb Bi N 0

1 Invention example 0.009 0.007 1.540 0.071 0.502 0.0098 0.0167 0.0178

2 Invention example 0.0018 0. 012 1.512 0. 078 0. 494 0. 0063 0. 014-0. 0176 0. 0190

3 Invention example 0.0008 0. 008 1. 090 0. 090 0. 530 0. 0075 0. 016-0.000099 0.

4 Invention example 0.0014 0.015 1.688 0.080 0.550 0.0039 0.009 0.0020 0000.0083 0.0179

5 Comparative example 0.011 0. 013 1.410 0. 074 0. 458 0. 0111 0. 0165

6 Comparative Example 0.019 0.013 1.430 0.071 0.468 0.029 0.0131 0.01159

7 Invention example 0.051 0, 013 1.606 0. 079 0. 526 0. 0064 0. 0091 0. 0173

8 Inventive example 0, 024 0.004 1.429 0. 077 0. 467 0. 1181 0. 0143 0. 0198

9 Invention example 0.036 0.005 1.471 0.082 0.481 0.44462 1 0.0083 0.0201

10 Invention example 0.057 0.007 0.919 0, 081 0.452 0.0054 0.0030 0.0094 0.0183

11 Inventive example 0.057 0. 011 1.651 0. 079 0.540 0.0058 0.013 0.0126 0.0191

12 Illustrative example 0.023 0.010 0.988 0.076 0.476 0.0070 0.015 0.0165 0.0183

13 Inventive example 0.050 0.005 005 1.409 0. 081 0.459 0.0067 0.015 0.0024 0.0126 0, 0196

14 Comparative Example 0.024 0.00.09 1.424 0.082 0.464 0.0132 0.0150

15 Invention example 0.076 0.010 0.983 0.074 0.322 0.0051 _ 0.0103 0.0197

16 Invention example 0.071 0.003 0.897 0.077 0.299 0.0034 0.007 1 0.0117 0.0198

17 Invention example 0.073 0.003 0.909 0.077 0.300 0.0049 0.Oil 0.0034 0.0098 0.0200

18 Invention example 0.083 0.007 0.861 0.088 0.287 0.0059 0.275 0.0137 0.0151

19 Invention example 0.072 0.004 0.907 0.071 0.297 0.0092 0.020-1.271.0.0143 0.0177

20 Invention example 0.084 0.014 1.002 0.071 0.331 0.0085 0.019 0.0027 0.186 0.0142 0.0186

21 Inventive example 0.078 0. 013 0.889 0.085 0.292 0.0049-0.113 0.0084 0.0199

22 Comparative Example 0.079 0.014 1.068 0.089 0.348 0.0145 0.0202

23 Comparative Example 0.080 0.003 1.065 0.075 0, 347 0.279 0.0119 0.0186

24 Comparative Example 0.071 0.010 0.909 0.072 0.299 0.177 0.0178 0.0157

25 Comparative example 0.071 0.002 0.911 0.089 0.300 0.119 0.0120 0.0208

26 Comparative Example 0.076 0.004 1.59 0.084 0.479 0.057 0.0099 0.0171

27 Invention example 0.073 0.012 1.533 0.073 0.503 0.0039 0.0104 0.0197

28 Invention example 0.073 0.008 1.426 0.086 0.465 0.0079 0.009 0.0131 0.0182

29 Invention example 0.073 0.005 1.013 0.085 0.491 0.0070 0.017 0.0119 0.0200

30 Inventive example 0.079 0.007 1.589 0.072 0.521 0.0066 0.017 0.0028 0.0130 0.0194

31 Comparative Example 0.087 0.015 1.624 0.082 0.530 0.0176 0.0165

32 Inventive example 0.080 0.002 2.204 0.079 0.720 0.0046 0.0146 0.0152

33 Inventive example 0.079 0.Oil 2.188 0.082 0.712 0.0060 0.0090 0.0202

34 Invention example 0.088 0.002 2.147 0.084 0.699 0.0088 0.010 0.0105 0.0155

35 Inventive example 0.081 0.014 2.203 0.078 0.717 0.0035 0.019 0.0018 0.0140 0.0204

36 Comparative Example 0.077 0.003 2.056 0.077 0.672 0. 0141 0.0189

37 Invention Example 0.075 0.012 0.332 0.083 0.087 0.0043 0.0142 0.0206

38 Invention example 0.081 0.002 0.346 0.089 0.088 0.0095 0.020 0.0163 0.0169

39 Invention Example 0.078 0.006 0.384 0.087 0.096 0.0056 0.012 0.0017 0.0129 0.0177

40 Comparative Example 0.071 0. 012 0. 326 0. 090 0, 083 0. 0178 0. 0174 Table 2

Table 3

Table 4

All of the inventive examples were superior to the comparative example in terms of drill tool life, and had good surface roughness in plunge cutting. This is because even if the addition amounts of C, S, etc. are different, the order does not change. When elements such as Zn, Sn, B, etc. are added, the tool life and Excellent surface roughness. The higher the S content, the better the machinability, but even when the S content was relatively small, the chip controllability was improved.

On the other hand, even when Sn was added as in Comparative Examples 6 and 26 in the examples, machinability was not improved unless Zn was added.

In addition, even when conventional machinability-improving elements such as Te, Pb, and Bi were included, the addition of Z η showed better machinability. Table 5 shows the chemical composition of the sample evaluated for the machinability and mechanical properties of the steel based on, and Table 6 shows the evaluation results. A part of each specimen was melted in a 270 t converter, then disassembled and rolled into billets, and further rolled into φ65 mm steel bars. The others were melted and rolled in a 2 t vacuum melting furnace. Impact value (JZ cm ² was evaluated by preparing a U-notch specimen with a depth of 2 according to JIS.

Table 3 shows the cutting conditions in the drilling test for the machinability evaluation of Examples 41 to 43 containing about 0.1% C. The machinability was evaluated at the highest cutting speed (so-called VL1000) capable of cutting up to the accumulated hole depth lOOOOmin.

Furthermore, the surface roughness was evaluated by so-called plunge cutting, in which the tool shape was transferred by a parting-off tool. In the experiment, we measured the surface roughness when machining 200 grooves. The surface roughness was evaluated by the plunge cutting shown in Table 4.

For Examples 44-46 containing about 0.3% C and Examples 47-77 with more C content, the impact value and its anisotropy were shown in order to emphasize the mechanical properties. Here, the impact value of the sample cut out from the cross section direction of the steel bar is shown (“C direction” column), and (an impact value of the transverse direction sample) / (an impact value of the longitudinal sample) is shown as anisotropy. ("Anisotropic" column). The larger the value is, the smaller the anisotropy is. The evaluation of the machinability of Examples 47 to 77 was carried out with the drilling property VL1000, and evaluated under the cutting conditions shown in Table 7. In these cases, the cutting surface roughness was not evaluated.

Table 6

Example Machinability Hardness

No. Category VL1000 Surface roughness HV C direction Anisotropy

41 Invention example 65 20. 3 128 —

42 Invention 65 21. 2 132--

43 Comparative Example 45 33. 5 132 — —

44 Invention example 52 — 167 53. 4 0.55

45 Invention Example 57 — 165 53. 4 0.53

46 Comparative Example 43 ― 174 52.1 0.55

47 Invention Example 47 1 194 41.6.0.52

48 Invention 50 184 38.1 0.55

49 Comparative Example 37 196 38.0 0.59

50 Invention example 44 1 206 36.2 0.45

51 Invention 36-215 35.3 0.46

52 Comparative Example 25 ― 203 35.9 0.48

53 Comparative Example 46 ― 199 18.9 0.29

54 Invention 45 210 35.4 0.44

55 Invention 37 37 202 37.3 0.58

56 Comparative Example 26 1 208 36.9 0.53

57 Invention 43-206 36.6 0.55

58 Invention Example 44 ― 212 35.9 0.51

59 Comparative Example 26 ― 212 37.7 0.51

60 Invention 38-201 37.3 0.55

61 Invention example 42 ― 205 35.9 0.46

62 Comparative Example 25 ― 202 36.4 0.45

63 Invention example 45 198 41.4 4 0.63

64 Invention 50-192 39.8 0.52

65 Comparative Example 34 — 193 41. 4 0.54

66 Inventive example 50 — 202 41.5 0.66

67 Invention 50-192 39.0 0.53

68 Comparative Example 35 196 41. 2 0.54

69 Invention 46-205 38.5 0.51

70 Inventive example 48 204 40.0 0.64

71 Comparative Example 31 201 39.6 0.55

72 Invention example 48 06 40.4 0.59

73 Invention 48 192 38.7 0.50

74 Comparative Example 31 208 38.6 0.48

75 Invention 47 193 38.9 0.59

76 Invention example 48 205 41.2 0.52

77 Comparative Example 35 203 40.4 0.64 Table 7

In the comparison of Example 41 43, the inventive example outperformed the comparative example in VL1000 and surface roughness. Also, with regard to Example 4477, the invention example shows a hardness HV, an impact value of the sample in the cross section direction and an impact value of the sample in the cross section direction of the comparative example containing substantially the same C and other alloying elements. Although the impact value of the sample in the longitudinal direction is almost the same,

It can be seen that VL1000 is good and has excellent machinability.

Furthermore, when the machinability was improved by increasing the amount of S as in Comparative Example 53, the anisotropy of the impact value was reduced, and the performance as structural steel was considered to be inferior to that of Invention Example 47 48. Was.

Table 8 shows examples in which a large amount of alloying elements were added to improve the hardenability of steel. Some of the test materials were melted in a 270 t converter, then disassembled and rolled into billets, and further rolled to φ50 mm. The others were melted and rolled in a 2 t vacuum melting furnace.

In Example 7882, a steel based on SCr420 was subjected to normalization (920 ° C x lhr → air cooling) and then subjected to a cutting test. The machinability was evaluated in a drilling test with the same cutting conditions as in Table 5, and the evaluation item was the highest cutting speed (so-called VL1000) that could be cut up to a cumulative hole depth of 1000 mm. The unit of this VL1000 is m / min. The larger the value, the better the tool life. In addition to measuring the hardness, as shown in Fig. 2, an Ono-type rotary bending test piece with a notch formed with a notch of R 1.16 on a 9 mm diameter test piece was prepared, and Figs. 3 (a) and ( b) Fatigue properties were evaluated after carburizing under the conditions shown in b). As a result, although the hardness after normalizing shown in Fig. 3 (b) was almost the same, the developed steel was superior to VL1000. The fatigue characteristics after carburization are almost the same, and it can be seen that the technology of the present invention improves machinability but does not lower the subsequent gear performance.

Table 8

Examples Chemical components (mass%) Machinability Hardness Fatigue limit

No. Category C 'Si Mn P s Zn Sn B Cr Al N 0 VLIOOO HV MPa

78 Invention example 0.21 0.19 0.71 0.016 0.013 0.0075 1.05 0.032 0.0056 0.0021 66 157 499

79 Invention example 0.20 0.19 0.70 0.018 0.017 0.0032 0.0027 0.94 0.034 0.0050 0.0059 70 153 505

80 Invention Example 0.18 0.19 0.72 0.014 0.013 0.0078 0.0163 1.09 0.032 0.0045 0.0056 72 149 496

81 Comparative Example 0.21 0.19 0.79 0.020 0.013 0.94 0.026 0.0056 0.0052 54 150 502

82 Comparative Example 0.19 0.19 0.71 0.016 0.046 0.91 0.018 0.0060 0.0042 73 149 485

Table 9 shows examples based on steel with improved hardenability by further adding a large amount of alloying elements. A part of the test material was melted in a 270 t converter, then disassembled and rolled into billets, and further rolled to φ50 mm. The others were melted and rolled in a 2 t vacuum melting furnace. The machinability was evaluated by a drilling test and the cutting conditions were the same as in Table 7, and the evaluation item was the highest cutting speed (so-called VL1000) capable of cutting to a cumulative hole depth of 1000.

In Examples 83 to 88, the hardness was adjusted to about HV310 by quenching and tempering using SCM440 as a base steel, and the machinability was evaluated with VL1000. The impact value was evaluated as a mechanical property. The impact value was measured by cutting a sample from the longitudinal direction of the bar and using a JIS3 test piece (2 mmU notch test piece). As a result, although the invention example had almost the same hardness and impact value (J / cm ² ) as the comparative example, the machinability VL1000 was larger and superior to the comparative example.

In Examples 89 to 94, the bearing steel was used as a base, and the steel was softened by spheroidizing annealing at 700 ° C for 20 hours, and the machinability VL1000 was measured. As a result, although the invention example had almost the same hardness as the comparative example, the machinability VL1000 was large and was superior to the comparative example.

Table 9

Example I-Dakugaku component (mass96) Machinability Hardness Impact value

No. Category C Si Mn Ps Zn Sn B Cr Mo W Ni Cu Al N 0 VLIOOO HV Longitudinal direction

83 Invention Example 0.39 0.19 0.75 0.013 0.017 0.0067 1.02 0.17 0.026 0.0053 0.0013 13 315 61.8

84 Inventive example 0.40 0.20 0.74 0.013 0.017 0.0065 0.0148 0.97 0.22 0.031 0.0064 0.0015 10 309 77.3

85 Comparative Example 0.43 0.19 0.74 0.013 0.016 0.91 0.28 0.018 0.0046 0.0017 7 308 64.9

86 Inventive example 0.39 0.21 0.72 0.013 0.019 0.0094 1.10 0.33 0.033 0.0060 0.0016 13 307 75.3

87 Inventive example 0.42 0.21 0.71 0.014 0.018 0.0098 0.0207 1.07 0.29 0.021 0.0055 0.0014 12 317 69.5

88 Comparative Example 0.39 0.19 0.79 0.013 0.018 0.95 0.21 0.016 0.0052 0.0014 8 305 70.9

89 Invention example 0.22 0.22 0.59 0.018 0.020 0.0034 0.48

to 0.17 1.82 0.030 0.0055 0.0036 34 266 107.4

90 Invention 0.19 0.19 0.55 0.017 0.014 0.0062 0.0024 0.47 0.24 1.76 0.10 0.021 0.0050 0.0030 35 273 101.5

91 Comparative Example 0.20 0.18 0.57 0.017 0.016 0.46 0.25 1.83 0.09 0.026 0.0056 0.0051 29 275 105.9

92 Inventive example 0.98 0.30 0.51 0.028 0.027 0.0058 1.50 0.029 0.0065 0.0009 24 276

93 Inventive example 0.98 0.33 0.53 0.018 0.020 0.0099 0.0213 1.44 0.034 0.0056 0.0009 23 272

94 Comparative Example 0.99 0.21 0.52 0.017 0.024 1.49 0.019 0.0045 0.0011 15 271

Industrial applicability

According to the steel of the present invention, by promoting the fracture of the matrix in the steel,

For so-called low-carbon free-cutting steel with a C content of less than 0.15%, tool life and cutting surface roughness can be improved, and good tool life and cutting surface roughness can be obtained even without Pb. Even for structural steels containing 0.15% or more of C, machinability can be improved and mechanical properties, especially anisotropy, can be minimized. Alternatively, the steel of the present invention can obtain better machinability than steel having similar mechanical properties.

Claims

The scope of the claims

1. In mass%,

C: 0.001-1.5%,

Si: 3% or less,

Mn: 0.01-3%,

P: 0.001 to 0.2%,

S: 0.0001-1.2%,

Zn: 0.00 ;! ~ 0.5%,

N: 0.0001-0.02%,

O: 0.0005-0.05%

Excellent machinability steel characterized by containing.

2. The steel with excellent machinability according to claim 1, further comprising Sn: 0.002 to 0.5% at a mass of ⁰ / o.

3. The steel with excellent machinability according to claim 1 or 2, further comprising B: 0.0005 to 0.05% by mass%.

4. In addition, in mass%,

Cr: 0.01-7%,

Mo: 0.01-3%,

V: 0.0:! ~ 3%,

Nb: 0.001 to 0.2%,

Ti: 0.001-0.5%,

W: 0.0 :! ~ 3%

The steel with excellent machinability according to any one of claims 1 to 3, wherein the steel comprises one or more of the following.

5. In addition, the mass ^{_{0/0, Ni: 0.05~ 7}} %, Cu: with containing 1 'species or two of 0.02 to 3%, if the Cu contains more than 0.3% Ni% The steel with excellent machinability according to any one of claims 1 to 4, wherein the steel satisfies ≥Cu%.

6. In addition, in mass%,

A1: 0.001 to 2%,

Ca: 0.0002-0.01%,

Zr: 0.0003-0.5%,

Mg: 0.0002-0.02%

The steel excellent in machinability according to any one of claims 1 to 5, wherein the steel comprises one or more of the following.

7. In addition, in mass%,

Te: 0.001 to 0.5%,

Pb: 0.01 to 0.7%,

Bi: 0.01 to 0.7%

The steel with excellent machinability according to any one of claims 1 to 6, wherein the steel comprises one or more of the following.